Control for rock drill mounting



April 20, 1965 E. H. KURT 3,179,015

CONTROL FOR ROCK DRILL MOUNTING Filed Feb. 11, 1963 6 Sheets-Sheet 1 4 I 33 34 r 2 '4 v 2 L l6 3e 7J F/GJ M 22 my I IHJI'I 3 g9 i INVENTOR. 1M4 EwALmH/rz/Rr I BY J April 20, 1965' E. H. KURT 3,179,015

CONTROL FOR ROCK DRILL MOUNTING Filed Feb. 11, 1963 6 Sheets-Sheet 2 FIG. 4

INVENTOR. E WALD H KURT ATTO EY A ril 20, 1965 E. H. KURT 3,

CONTROL FOR ROCK DRILL MOUNTING Filed Feb. 11, 1963 6 Sheets-Sheet 3 6 INVENTOR 5 v EWAYLD H. KURT AT EY April 20, 1965 EH. KURT CONTROL FOI R ROGK DRILL MOUNTING 6 Sheets-Sheet 4 Filed Feb. 11, 1963 Ill INVENTOR EWALD H KUR April 20, 1965 E. H. KURT CONTROL FOR ROCK DRILL MOUNTING 6 Sheets-Sheet 5 Filed Feb. 11, 1963 A TORNEY April 20, 1965 KURT 3,179,015

CONTROL FOR ROCK DRILL MOUNTING Filed Feb. 11, 1963 6 Sheets-Sheet 6 66 INVENTOR RT EW4YLD H KU AT RNEY United States Patent 3,179,015 CONTROL FOR ROCK DRILL MOUNTING Ewald H. Kurt, Philllpsburg, N..l., assignor to Ingersoll- Rand Company, New York, N.Y., a corporation of New Jersey Filed Feb. 11, 1963, Ser. No. 257,564 10 Claims. (Cl. 91-172 This invention relates to rock drilling apparatus and more particularly to an arrangement for adjusting the position of the rock drill mounted on the rock drilling apparatus relative to the rock face.

In rock drilling apparatus of the type provided with a swingable boom, a support for the rock drill of the rock drilling apparatus is mounted adjustably on the extreme end of the boom, the said support being adapted to provide for movement of the rock drill into various drilling positions with respect to the rock face. In the construction of such boom type rock drilling apparatus, a common expedient for adjusting the position of the rock drill support mounted on the end of the boom consists of a gear arrangement by means of which the rock drill support is caused to roll about the end of the boom to properly position the rock drill for drilling operations. Inasmuch as the rock drill and its guide are of considerable weight and length, any looseness in the components of the rock drill support, or clearance in the gearing, affects the efficiency of drilling. In addition, the backlash of the gears as a result of such clearance is harmful, causing breakage and other inconveniences.

It is an object of this invention to provide a rock drill mounting with an improved rock drill supporting arrangement to provide for greater efficiency of drilling than heretofore experienced.

Another object of this invention is to provide a rock drill mounting with which the rock drill is firmly held in drilling position.

Yet another object of this invention is to provide a rock drill mounting with which the rock drill is readily and expeditiously movable into various drilling positions.

Still another object of this invention is to provide a rock drill mounting with which the rock drill is firmly locked in drilling position.

Another object of this invention is to provide a rock drill mounting with which wear of the various components thereof is substantially reduced.

Other objects and advantages of the invention will be in part obvious and in part pointed out hereinafter.

The accompanying drawings illustrate two embodiments of the invention in which:

FIGURE 1 is a longitudinal section of one embodiment of the rock drill mounting according to the invention;

FIG. 2 is a cross-sectional view of FIG. 1 taken along the line 2-2 and looking in the direction of the arrows;

FIG. 3 is a sectional view of FIG. 2 taken along the line 33 and looking in the direction of the arrows;

FIG. 4 is a diagrammatical view of the pressure fluid control system as applied to the rock drill mounting shown in FIGS. 1-3;

FIG. 5 is a longitudinal section of another embodiment of the rock drill mounting;

FIG. 6 is a section taken along the line 6-6 of FIG. 5 looking in the direction of the arrows;

FIG. 7 is a section taken along the line 77 of FIG. 5 looking in the direction of the arrows; and

FIG. 8 is a diagrammatical view of the pressure fluid control system as applied to the rock drill mounting shown in FIGS. 57.

Since the invention does not reside in the entire rock drilling apparatus but in the mounting of the support for the rock drill on the outer end portion of the boom of the rock drilling apparatus, only that portion of the rock drilling apparatus is shown and described, the other portion of the rock drilling apparatus being of a well-known conventional design. The mounting according to the invention, as shown in FIGS. 1, 2 and 3, and FIGS. 5, 6 and 7, is designated 10 and includes a commonly known type boom 12 (partly shown), an extension element in the form of a pinion gear 14 rigidly connected to the end portion of boom 12, and a rock drill supporting member 16 in the form of a housing mounted rotatably on pinion gear 14, the latter being provided at its outer end portions with suitable sleeve bearings 18 and 20 for rotation of the rock drill supporting member 16 about pinion gear 14. A locking member 22 is mounted on the free end of pinion gear 14 to cooperate with the corresponding end portion of the rock drill supporting member 16 to hold the supporting member against axial movement. The free end portion of the rock drill supporting member 16 is in the form of a yoke 24, which is suitably formed for attachment to a swivel arrangement A upon which a rock drill (not shown) is mounted in a commonly known manner, see FIGS. 5 and 7.

A suitable gearing arrangement is provided to cause rotation of the rock drill supporting member 16, and therewith the rock drill swivel arrangement A, with respect to boom 12 to provide for adjustment of the drilling position of the rock drill (not shown). For this purpose pinion gear 14 connected to the outer end portion of boom 12 is engaged by a meshing rack gear 26 positioned transversely of pinion gear 14. Rack gear 26 is positioned between and connected to two opposing pistons 28, 30 to form an integral unit therewith. This unit is slidably housed in a cylinder 32 positioned transversely of the axis of pinion gear 14 and forming an integral part of the housing or rock drill supporting member 16 within which also pinion gear 14 is disposed. Each piston 28, 3% is provided with an end face exposed to hydraulic motive fluid, such as oil, introduced at either end of cylinder 32 depending upon the direction in which rock drill supporting member 16 is desired to be rotated with respect to boom 12.

When pressurized fluid is admitted either into the righthand side end portion of cylinder 32 or into the let hand side end portion of cylinder 32, the resultant forces exerted by the pressurized fluid in either one of the end portions of cylinder 32 cause cylinder 32 and rack gear 26 to rotate about pinion gear 14. Since cylinder 32 forms an integral part of the housing or rock drill supporting member 16, rotation of cylinder 32 and rack gear 26 results in rotation of the rock drill supporting member 16 about pinion gear 14 providing for adjustability of the rock drill swivel arrangement A relative to the boom.

When a desired drilling position of the rock drill (not shown) is reached, a common expedient to hold the rock drill supporting member against rotary motion is to prevent movement of rack gear 26 relative to pinion gear 14 by preventing the hydraulic fluid in each end portion of cylinder 32 from escaping therefrom. However, since there is clearance between the mating teeth of the rack gear 26 and the pinion gear 14, movement of the rack gear relative to the pinion gear and, consequently, movement of the drill supporting member relative to the pinion gear are unavoidable. Accordingly, when the rock drill operates, an injurious chattering of the gear teeth is produced, which chattering is a result of the rapid collisions between the associated gear teeth.

By this invention means is provided to eliminate such collisons between the gear teeth by insuring that the associated mating gear teeth are held constantly in engagement with each other and locked against movement with respect to each other during operation of the rock drill (not shown). For this purpose a locking arrangement in the form of a second rack gear 34 is provided in meshing relationship with pinion gear 14 and positioned to cooperate with rack gear 26 to provide for constant engagement between the associated mating teeth of rack gear 26 and pinion gear 1 As shown in FIGS. 1 and 2, a bore is provided in the unit formed by rack gear 26 and pistons 28, 39 to form cylinders 4d, 49 to slidably accommodate pistons 35, 3%, piston 36 being disposed within piston 2d, and piston 38 within piston 39. The rack gear 34 is positioned between and connected to the opposing pistons 36, 38 to form an integral unit therewith, the teeth of rack gear 34% meshing with the teeth of pinion gear 14. The teeth of rack gear 26 are formed in two rows transversely spaced from each other to engage the outer end portions of the teeth of pinion gear 14. In this manner a space is formed between the two rows of teeth of rack gear 26 to provide for the teeth of the locking rack gear 34 to engage the intermediate portion of pinion gear 14. Two passages 96 and 97 are formed in the wall of cylinder 40, passage 96 to communicate the cylinder space to the right of piston 28 with the cylinder space to the left of piston 33, and passage 97 to communicate the cylinder space to the left of piston 30 with the cylinder space to the right of piston 56, see FIG. 4. The purpose of passages 96, 97 will appear hereinafter.

A suitable hydraulic arrangement, as shown schematically in FIG. 4, is provided to adjust the position of the rock drill swivel arrangement A as well as to lock the associated gears against movement relative to each other to prevent backlash of the gears. The hydraulic arrangement comprises a pump P driven by a motor M to pump hydraulic fluid from a tank T through a discharge conduit 8% to a directional valve V3tl. Directional valve V30 is of a commonly known manually operated type and is connected to conduits 8t), 82, 38 and 2, the hydraulic fluid from discharge conduit 8% being directed selectively to either conduit 82 or conduit 88. The design of directional valve V3ll is such that, when conduit St is communicated with conduit 82, conduit 88 is automatically communicated with conduit 92 which is connected to tank T, and, when conduit 8i) is communicated with conduit 33, conduit 8?; is automatically communicated with conduit 92 and tank T. Conduits 82 and 88 are connected to control valves V10, VZti which in turn are connected to the end portions of cylinder 32. Each control valve V10, VZtl includes a spring-loaded ball type check valve and an operatively related spring loaded piston Pill, P20, respectively, each piston having opposing pressure surfaces of different areas exposed to hydraulic fluid pressure to cause the piston to force the associated check valve into an open position when necesary, as will be explained hereinafter.

When the rock drill supporting member is to be adjusted and rotated in a clockwise direction, directional valve V30 is set to communicate the discharge conduit 80 of pump P with conduit 82, and to communicate conduit 81; with conduit 92 and tank T. Pressurized hydraulic fluid is conducted from conduit fill to conduit 32,

past the check valve in valve V29, to conduit 84 and into the right-hand side of cylinder 32.. The pressurized fluid within the space to the right of piston 28 is further conducted through passage 96 to the space to the left of piston 38. Since the hydraulic fluid present in the space to the left of piston St is permitted to flow freely into tank T, as will be explained hereinafter, the action of the pressurized fluid within the space to the right of piston 28 results in cylinder 32 and the associated pistons and rack gears to rotate about pinion gear 14 in a clockwise direction, causing the space to the right of piston 28 to: increase while the space to the left of piston 36 decreases. During clockwise rotation of rack gear 34 about the pinion gear, the space to the left of piston 38 increases while the space to the right of piston 36 decreases. The hydraulic fiuid present in the decreasing spaces to the left of piston 3t and to the right of piston 36 is returned to tank T by flowing through passage Q7 and conduit 86 and into valve Vii past the check valve therein. The check valve is held in an open position by piston Pill which is actuated by pressurized fluid conducted to valve V10 from conduits 82 and 98. From valve Vlil the return fluid is conducted through conduits E8 and 92 into tank T.

When a desired drilling position is reached, directional valve V30 is closed to prevent communication between conduits S2 and 88 with conduits 8h 92, respectively, preventing the escape of hydraulic fluid from the spaces to the right of pistons Q8, 36 and to the left of pistons 39, 38. Cylinder 32, which supports the rock drill, is prevented from rotary movement relative to pinion 14 and boom 12. It is to be noted that the pressurized fluid in the space to the right of piston 23 urges piston 28 to the left causing rack gear 26 to engage pinion gear 14 from the right, while the pressurized fluid in the space to the left of piston 33 urges piston 38 to the right causing rack gear 34- to engage pinion gear 14 from the left. With the arrangement of constantly engaging pinion gear 14 by two opposing forces, movement of rack gears 2t; and 34 relative to pinion gear 14 is prevented and backlash of the associated gear teeth is eliminated.

When the rock drill supporting member is to be adjusted and rotated in a counter-clockwise direction, directional valve V30 is set to communicate the discharge conduit 8d of pump P with conduit 88, and to communicate conduit 82 with conduit 92 and tank T. Pressurized fluid is conducted from conduit 80 to conduits 88, 88, past the check valve in valve Vltl, conduit 36 and into the space to the left of piston 39. Pressurized fluid in the space to the left of piston 36 is further conducted through passage 97 into the space to the right of piston 36. Rotation of the rock drill support in a counterclockwise direction is effected and the spaces to the left of piston 30 and to the right of piston 36 increase while the spaces to the right of piston 28 and to the left of piston 33 decrease. Return flow of fluid from the decreasing space to the left of piston 38 is conducted through passage 5%? into the space to the right of piston 28, the return flow of fluid from the decreasing space to the right of piston 28 being conducted to tank T by Way of conduit 84, past the check valve in valve V20 which is held in an open position by the action of pressurized fluid admitted to valve V20 through conduits 94, 88, to actuate piston P20. From valve V29 the return fluid flows through conduit 82 and conduit 92 into tank T. When a desired drilling position is reached, directional valve V39 is closed to prevent the pistons and rack gears from movement relative to each other and relative to the pinion gear, as explained hereinbefore with respect to rotation of the rock drill support in a clockwise direction.

Another embodiment of the invention is shown in FIGS. 5, 6 and 7 in which the cylinder for the locking rack gear arrangement is positioned in a side-by-side relation with the cylinder for the rack gear arrangement for adjusting the position of the rock drill instead of the cylinde -withincylinder (or piston-within-piston) arrangement shown in FIGS. 1, 2 and 3. The arrangement of the pinion gear 14 and that part of housing 16 for the pinion gear as shown in FIGS. 5, 6 and 7 is identical to that described hereinbefore in connection with FIGS. 1, 2 and 3, the additional structure with respect to that shown in FIGS. 5, 6 and 7 being as follows: Two cylinders 32' and 40' are positioned side by side as a unit and connected transversely to the housing for pinion gear 14 to form an integral part therewith. Within cylinder 32 are slidably disposed two opposing pistons 28, 30' with a rack gear 26 positioned therebetween to engage one outer end portion of pinion gear 14. Within cylinder 40' are slidably disposed two opposing pistons 36', 38' with a rack gear 34' positioned therebetween to engage the other outer end portion of pinion gear 14.

A suitable hydraulic arrangement, as shown schematically in FIG. 8, is provided to adjust the position of the rock drill as Well as to lock the associated gear teeth against movement relative to each other to prevent backlash of the gear. The hydraulic arrangement comprises a pump P driven by a motor M to pump hydraulic fluid from a tank T through a discharge conduit 52 to a directional valve V5. Directional valve V5 is of a commonly known manually operated type and is connected to conduits 52, 54, 62 and 64, the hydraulic fluid from discharge conduit 52 being directed either to conduit 54 or conduit 62. The design of directional valve V5 is such that when conduit 52 is communicated with conduit 54, conduit 62 is automatically communicated with conduit 64 which is connected to tank T, and, when conduit 52 is communicated with conduit 62, conduit 54 is automatically communicated with conduit 64 and tank T. Conduits 54 and 62 are connected to control valves V1, V2, V3 and V4 which in turn are connected to the end portions of cylinders 32 and 40 to control the flow of hydraulic fluid thereto to actuate the rock drill supporting member as well as to lock the associated gear teeth against backlash. Each of the control valves V1, V2, V3 and V4 includes a springdoaded ball type check valve and an operatively related spring-loaded piston P1, P2, P3 and P4, respectively, each piston having opposing pressure surfaces of different areas exposed to hydraulic fluid to provide for actuation of the associated check valve into an open position when necessary, as will be explained hereinafter.

When the rock drill supporting member is to be adjusted and rotated in a counter-clockwise direction, directional valve V5 is set to communicate conduit 52 with conduit 54 to conduct pressurized hydraulic fluid, and to communicate conduit 62 with conduit 64 to conduct return fluid to tank T. Pressurized hydraulic fluid flows from conduit 52 to conduits 54 and 56 past the ball check valve of valve V2 to conduit 58 and into the right-hand side end portion of cylinder 32'. Simultaneously, pressurized hydraulic fluid from conduit 54 is introduced into the lefthand side end portion of cylinder 4t) by way of valve V1 past the check valve therein and conduit 68. As a result of the pressure of the pressurized hydraulic fluid exerted on the greater pressure area of piston 28 relative to the pressure area of piston 38', cylinder 32' and cylinder 40' as a unit with the rock drill supporting member move counter-clockwise about pinion gear 14 causing not only the space to the left of piston 30 but also the space to the left of piston 38 to decrease, thereby forcing out the hydraulic fluid present in the space to the left of piston 30, and the pressurized hydraulic fluid present to the left of piston 38. The pressurized fluid in the space to the left of piston 38' is forced into conduit 68 and is permitted to flow past the check valve in valve V1 because the check valve is forced into an open position by piston P1 of valve V1, piston P1 being forced to the left as a result of introducing pressurized fluid from conduit 54 through conduit 67 to the greater pressure area on the right-hand side of the piston P1 relative to the pressure area adjacent the check valve. The pressurized fluid from conduit 68 flows past the check valve in valve V1 into conduit 56 to be recirculated past the check valve in valve V2, conduit 58 and into the increasing space to the right of piston 28. The return fluid present in the decreasing space to the left of piston 30 flows through conduit 643 into valve V4 past the check valve which is held in an open position by the pressurized fluid conducted from conduit 58 through conduit 66 into valve V4 to cause piston P4 to hold the check valve in an open position. From valve V4 the hydraulic fluid flows through conduit 62, valve V5 into conduit 64 and tank T. As the space to the right of piston 36' is increasing, the hydraulic fluid therein is supplemented by drawing in hydraulic fluid from tank T by way of conduit 64, valve V5, conduit 62, past the check valve in valve V3, and conduit 79.

After a predetermined drilling position is reached, valve V5 is closed to prevent communication between conduits 54 and 52, and between conduits 62 and 64. The pressurized fluid in the spaces to the right of piston 28 and to the left of piston 38' and the return fluid to the right of piston 36 and to the left of piston 30' are trapped therein preventing backlash by maintaining constant opposing forces on pistons 28' and 38' for a constant engagement between the mating teeth of rack gears 26', 34'.

When the rock drill supporting member is to be rotated in a clockwise direction, valve V5 is adjusted to communicate conduit 52 with conduit 62, and to communicate conduit 64 and tank T with conduit 54. Pressurized hydraulic fluid is conducted to conduit 62, past the check valve in valve V4, to conduit 56, and into the left-hand side end portion of cylinder 32. Simultaneously, pressurized fluid is conducted from conduit 62 past the check valve in valve V3 through conduit and into the righthand side end portion of cylinder 49' for creating the opposing forces to prevent backlash as hereinbefore eX- plained with respect to counter-clockwise rotation of the rock drill supporting member. As cylinders 32', 40 rotate clockwise about the pinion gear, the spaces to the left of pistons 39' and 38 increase while the spaces to the right of pistons 28' and 36' decrease. The pressurized fluid being forced out of the decreasing space to the right of piston 36' is conducted through conduit 70 into valve V3 past the check valve therein which is being held in an open position by piston P3, then to valve V4 past the check valve therein and through conduit 60 into the increasing space to the left of piston 30'. Return fluid from the decreasing space to the right of piston 28 is conducted through conduit 58 into valve V2 past the check valve therein which is being held in an open position by piston P2, then to conduits 56, 54 and into tank T by way of valve V5 and conduit 64. The hydraulic fluid in the increasing space to the left of piston 38' is supplemented by drawing in fluid from tank T by way of conduit 64, valve V5, conduit 54, past the check valve in valve V1, and conduit 68. When a desired drilling position is reached, valve V5 is closed to prevent communication between conduits 62 and 52, and between conduits 64 and 54 to maintain the constant opposing forces on pinion gear 14 for the prevention of backlash as explained hereinbefore.

Thus by the above construction are accomplished among others the objects hereinbefore referred to.

While two preferred embodiments of the invention are shown and described, it is understood that various changes and modifications may be made therein without departing from the scope of the invention.

I claim:

1. A transmission mechanism for a rock drill mounting having a drill support member mounted on a boom for movement relative to the latter, said transmission mechanism comprising:

(a) a pinion rigidly connected to the boom member and axially aligned therewith, (b) a casing connected to the rock drill support memher and rotatably mounted on said boom member to rotate about said pinion,

(c) a first rack. positioned in said casing and connected to two opposing pistons,

(d) said first rack being in mesh With said pinion, (e) a first pair of opposing cylinders for the pistons of said first rack formed in said casing, (f) a second rack positioned in said casing in meshing relationship with said pinion and mounted between member in the opposite direction, and simultaneously controlling the flow of the pressure fluid to one of said cylinders and the associated piston of said second rack to cause said second rack to urge said pinion in said opposite direction and maintain Cit e3 engagement between the associated teeth of said racks and said pinion and thus prevent the backlash of said racks relative to said pinion.

4. A transmission mechanism comprising:

(a) a pinion rotatably mounted on a support;

(b) a casing mounted on the support to house said pinion;

(c) a rack in said casing positioned to mesh with said pinion;

and connected to two opposing pistons, both of said (d) a first double-acting hydraulic motor in said casracks being located to simultaneously engage the ing operatively associated with said rack to urge said same teeth on said pinion, rack in one direction to cause said casing to rotate (g) each of said pistons associated With said first rack in the opposite direction about said pinion;

having a coaxial bore to form opposing cylinders (e) a second rack in said casing positioned to mesh for said pistons associated with said second rack, 5 with said pinion;

(h)a groove formed in said first rack to receive said (7) both of said racks being located to simultaneously second rack, and engage the same teeth on said pinion;

(i) means for controlling the flow of the pressure fluid (g) a second double-acting hydraulic motor in said to said cylinders and for causing said first rack to casing operatively associated with said second rack urge said pinion in one direction and effect rotation to urge said second rack in engagement with said of said casing and said rock drill support member in pinion, said second hydraulic motor being able to the opposite direction, and for causing said second apply substantially less force to said second rack rack to urge said pinion in said opposite direction to than said first hydraulic motor applies to said first prevent the backlash of said racks relative to said rack when both motors are supplied with equal hypinion. draulic pressures; and

2. The device claimed in claim 1 in which: (h) control means for said motors to efiect the urging (a) said means to conduct the pressure fluid to said of said racks simultaneously in opposite directions cylinders includes passage means to communicate the relative to each other and relative to said pinion and cylinder associated with the piston connected to one thereby maintain engagement between the associated end of said first rack with the cylinder formed in teeth of said racks and said pinion to prevent the the piston connected to the other end of said first backlash of said racks relative to said pinion while rack and to communicate the cylinder associated said first hydraulic motor overcomes said second with the piston connected to said other end of said motor and causes the pinion to rotate relative to first rack with the cylinder formed in the piston consaid support. nected to said one end of said first rack. 5. A transmission mechanism comprising:

3. A transmission mechanism for a rock drill mounting (a) a pinion rotatably mounted on a support;

having a drill support member mounted on a boom for (b) a casing mounted on the support; movement relative to the latter, said transmission mech- (c) a first rack positioned in meshing relationship with anism comprising: said pinion and mounted between and connected to (a) a pinion rigidly connected to said boom member 410 two opposing pistons;

and axially aligned therewith, (d) a first pair of opposing cylinders for the pistons (b) a casing connected to the rock drill support memof said first rack formed in said casing;

her and rotatably mounted on said boom member to (e) a second rack positioned in meshing relationship rotate about said pinion, with said pinion and mounted between and connected (c) a first rack positioned to mesh with said pinion and to two opposing pistons;

mounted between two opposing pistons to form a (f) both of said racks being located to simultaneously unit therewith, engage the same teeth on said pinion;

(d) a first pair of opposing cylinders for the pistons (g) a second pair of opposing cylinders for the pistons of said first rack formed in said casing, of said second rack formed in said casing;

(e) a second rack positioned to mesh with said pinion (h) means to conduct pressure fluid toisaid cylinders;

and mounted between two opposing pistons to form and aunit therewith, (i) means for controlling the flow of the pressure (f) each of said pistons associated with said first rack fluid to said cylinders to urge said first rack in one and having a coaxial bore to form opposing cylinders direction against the pinion and to simultaneously for said pistons associated with said second rack, urge said second rack in the other direction against (g) a groove formed in said first rack to receive said said pinion with a difierential force relative to said second rack, first rack whereby one of said racks overcomes the (h) passage means to communicate the cylinder assoopposing force of the other rack to cause said pinion ciated with the piston connected to one end of said to rotate While preventing the backlash of said racks first rack with the cylinder formed in the piston conrelative to said pinion. nected to the other end of said first rack and to com- 6. The transmission mechanism of claim 5 wherein: municate the cylinder associated with the piston con- (a) the opposing pistons of said second rack have nected to said other end of said first rack with the a substantially smaller hydraulic actuating area than cylinder formed in the piston connected to said one the pistons of said first rack so that the application 6nd of Said first Tack, and 5 of equal hydraulic pressures to the pistons of both (1) means for controlling the flow of the pressure fluid racks causes the first rack to overcome the second to one of said cylinders and the associated piston rack to rotate said pinion. of said first rack to cause said first rack to urge 7. The transmission mechanism of claim 6 wherein: said pinion in one direction and thereby eifect ro- (a) said racks are mounted side-by-side in said casing. tation of said casing and said rock drill support 8. The transmission mechanism of claim 6 wherein:

(a) said second rack is slidablylmounted in said first rack.

9. The transmission mechanism of claim 8 wherein:

(a) said second pair of opposing cylinders is formed in sai fi st ac 9 10 10. The transmission mechanism of claim 9 wherein: 2,524,488 10/50 Stevens 91-172 (a) said first rack contains passages interconnecting 2,844,128 7/58 Steiner 92136 each of the first pair of cylinders with a cylinder of 2,946,320 7/60 Vogel 91186 the second pair of cylinders with the thus intercon- 3,021,099 2/62 Samhamrner 91-44 nected cylinders acting in opposite directions. 5 3,030,713 4/62 Hendrickson 173-43 3,040,717 6/62 Rumsey 91-486 References Cited by the Examiner FOREIGN PATENTS UNIlED STATES PATENTS 639,877 7/50 Great Britain. 1,756,307 4/30 Rowntree 91-172 10 2,192,175 3/40 Ballard 92-138 FRED E. ENGELTHALER, Primary Examiner. 2,254,935 9/41 Darling 91411 2,436,190 2/48 Boisseau 91 172 SAMUEL LEVINE Examme" 

1. A TRANSMISSION MECHANISM FOR A ROCK DRILL MOUNTING HAVING A DRILL SUPPORT MEMBER MOUNTED ON A BOOM FOR MOVEMENT RELATIVE TO THE LATTER, SAID TRANSMISSION MECHANISM COMPRISING: (A) A PINION RIGIDLY CONNECTED TO THE BOOM MEMBER AND AXIALLY ALIGNED THEREWITH, (B) A CASING CONNECTED TO THE ROCK DRILL SUPPORT MEMBER AND ROTATABLY MOUNTED ON SAID BOOM MEMBER TO ROTATE ABOUT SAID PINION, (C) A FIRST RACK POSITIONED IN SAID CASING AND CONNECTED TO TWO OPPOSING PISTONS, (D) SAID FIRST RACK BEING IN MESH WITH SAID PINION, (E) A FIRST PAIR OF OPPOSING CYLINDERS FOR THE PISTONS OF SAID FIRST RACK FORMED IN SAID CASING, (F) A SECOND RACK POSITIONED IN SAID CASING IN MESHING RELATIONSHIP WITH SAID PINION AND MOUNTED BETWEEN AND CONNECTED TO TWO OPPOSITE PISTONS, BOTH OF SAID RACKS BEING LOCATED TO SIMULTANEOUSLY ENGAGE THE SAME TEETH ON SAID PINION, (G) EACH OF SAID PISTONS ASSOCIATED WITH SAID FIRST RACK HAVING A COAXIAL BORE TO FORM OPPOSING CYLINDERS FOR SAID PISTONS ASSOCIATED WITH SAID SECOND RACK, (H) A GROOVE FORMED IN SAID FIRST RACK TO RECEIVE SAID SECOND RACK, AND (I) MEANS FOR CONTROLLING THE FLOW OF THE PRESSURE FLUID TO SAID CYLINDERS AND FOR CAUSING SAID FIRST RACK TO URGE SAID PINION IN ONE DIRECTION AND EFFECT ROTATION OF SAID CASING AND SAID ROCK DRILL SUPPORT MEMBER IN THE OPPOSITE DIRECTION, AND FOR CAUSING SAID SECOND RACK TO URGE SAID PINION IN SAID OPPOSITE DIRECTION TO PREVENT THE BACKLASH OF SAID RACKS RELATIVE TO SAID PINION. 